Apparatus for evaporating and/or superheating a medium

ABSTRACT

A device for evaporating and/or superheating a medium, in particular a hydrocarbon or a hydrocarbon/water mixture for a gas generation system of a fuel-cell plant, includes a heat exchanger. The heat exchanger has, in its media-side region, at least one pair of films and in each case an inlet orifice and an outlet orifice which are connected in each case to a media space between the two films of the at least one pair of films. The media-side region is in thermally conductive contact with a region located on the heat transfer medium side. The media space is formed between the two films by depressions introduced on the medium-facing side of at least one of the films. The surface, facing away from the medium, in each case of at least one of the films of the at least one pair of films is provided with heat conducting ribs, the height of the heat conducting ribs being greater than the depth of the depressions.

BACKGROUND AND SUMMARY OF THE INVENTION

[0001] This application claims the priority of German patent document 100 03 273.7, filed Jan. 26, 2000, the disclosure of which is expressly incorporated by reference herein.

[0002] The present invention relates to an apparatus for evaporating and/or superheating a medium.

[0003] German patent document DE 44 26 692 C1 discloses a two-stage evaporating unit for converting a liquid reactant mass flow, which is adjustable as a function of a load presetting, into a gaseous reactant mass flow. With the aid of a heat transfer medium the liquid reactant mass flow is at least partially evaporated in the first stage and, if appropriate, completely evaporated in the second stage. Subsequently it is superheated. The evaporator unit is formed by an alternating stacking one on the other of films with heat transfer medium ducts and of films with reaction ducts.

[0004] Other known heat exchangers which may be used as an evaporator unit include, for example, plate heat exchangers with shaped metal sheets having a corrugated structure, bar/plate or plate/fin heat exchangers or laminated heat exchangers. Heating may take place by means of liquid and/or gaseous media.

[0005] Particularly when used in the evaporation of hydrocarbons or hydrocarbon/water mixtures, such as, for example, are employed for gas generation systems, the operation of evaporators of this type is problematic. Since abrupt load changes occur frequently, especially in mobile plants, the abovementioned evaporators can be used here only to a limited extent. That is, by virtue of their design, they ensure proper functioning predominantly in stationary operation, but are often unsuitable for dynamic operation because response times are too long.

[0006] The object of the present invention is to provide a simple and easily implementable design of a device for evaporating and/or superheating a medium.

[0007] Another object of the invention is to provide such a device which can evaporate the respective media quantity efficiently and quickly, particularly under dynamic operating conditions.

[0008] Finally, still another object of the invention is to provide a heating apparatus which is simple and cost-effective in terms of its design and production.

[0009] These and other objects and advantages are achieved by the apparatus according to the invention in which a media space is formed from the two films of at least one pair of films, by introducing depressions into the surfaces of one or both of the respective films which face the medium. Such depressions may be formed, for example, by an etching method, or by a stripping or shaping machining of the respective films. This results in a comparatively small media space between the films, in which the medium introduced via the inlet orifice can be evaporated and/or superheated, with insignificant idle times, even in the case of pronounced load jumps in the volume flow of the medium.

[0010] In order to implement the desired output of the evaporation device, the number of installed pairs of films can simply be increased, until the desired output can be transmitted.

[0011] At the same time, heat conducting ribs are provided on the surfaces facing away from the medium, of at least one of the films of the pair of films. When a plurality of pairs of films are used, pairs of films and heat conducting ribs can thus in each case be stacked alternately one above the other and connected to one another. A particularly advantageous manufacturing method which may be used for this purpose is soldering. The heat conducting ribs serve, in particular, for increasing the heat transmission surface and for the generation of turbulence.

[0012] On account of the size differences between the dimension of the heat conducting ribs and the depressions in the media space, the device according to the invention for evaporating and/or superheating a medium is particularly suitable for evaporating and/or superheating small media quantities per pair of films. By virtue of the much larger heat conducting ribs on or between the respective pairs of films, this can be carried out by means of thermal energy from a comparatively large volume flow of a heat transfer medium.

[0013] In this case, the heat transfer medium flowing through the device on the heat transfer medium side may be, in particular, a hot gas which flows around the pairs of films with a very much larger volume flow than that of the medium to be evaporated, and at the same time flows through the respective heat conducting ribs. In this case, this, for example, hot gas flow can discharge a large part of its thermal energy to the heat conducting ribs and consequently to the films which are in thermally conductive contact with the heat conducting ribs. Thus, this thermal energy is transmitted to the medium located in the media space between the two films of the at least one pair of films.

[0014] The invention consequently provides an ideal combination of a comparatively small media-side region of the heat exchanger with as large a region of the heat exchanger as possible on the heat transfer medium side. Very high dynamics and a very rapid evaporation of quantities of medium which vary abruptly are therefore possible. At the same time, the pressure loss is low on the heat transfer medium side. Overall, high Reynolds numbers or heat transmission coefficients can be achieved.

[0015] Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 shows a cross section through a device according to the invention for evaporating and/or superheating a medium;

[0017]FIG. 2 shows an enlargement of a detail corresponding to the area II in FIG. 1; and

[0018]FIG. 3 shows a longitudinal section through the device according to the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 shows a heat exchanger 1 in cross section. As can also be seen later in FIG. 3, the heat exchanger 1 is designed as a self-supporting structural element and is suspended in a housing 4 via two conduit elements 2, 3. The conduit element 2 forms the inlet orifice for a medium B to be evaporated, while the conduit element 3 forms the outlet orifice for the vapor B′. The media-side region of the heat exchanger 1 itself is formed by pairs of films 5, with heat conducting ribs 6 arranged between pairs of films 5.

[0020] The design of the heat exchanger 1 can be seen clearly in FIG. 2 in an enlarged detail. Each pair of films is composed of two films 5 a, 5 b, between which is located a media space 7 formed via numerous depressions 8 in the film 5 b. The media space 7 of each pair of films 5 is connected to the conduit elements 2 and 3 forming the inlet orifice and the outlet orifice respectively.

[0021] In the exemplary embodiment illustrated in FIG. 2, the media space 7 is formed via depressions 8 introduced (for example etched) into the film 5 b. It is of course, also possible in principle, to form the media space 7 via depressions 8 introduced into the film 5 a or into both the film 5 a and the film 5 b.

[0022] Particularly when the depressions 8 are produced by means of an etching, stripping or shaping method, the shape, size and depth and also the surface layout of the depressions 8 in the respective film 5 b and/or 5 a can be configured virtually almost as desired and can be produced in a simple way.

[0023] The heat conducting ribs 6 are mounted on the surfaces 9 facing away from the media space, and are in thermally conductive contact with the respective films 5 a, 5 b. This can be implemented, for example, by soldering. In the exemplary embodiment illustrated, the heat conducting ribs are formed from elements which are inserted between the individual pairs of films and which resemble corrugated metal sheets. In principle, any other embodiments, such as, for example, ribs, bosses, cones or the like soldered onto the pairs of films, would also be conceivable.

[0024] Between the pairs of films 5 and the heat conducting ribs 6 are formed cavities 10, which form that region of the heat exchanger 1 which is on the heat transfer medium side. A heat transfer medium, in particular a gaseous heat transfer medium A, can then flow through these cavities 10 perpendicularly to the plane of FIG. 2.

[0025]FIG. 3 shows a longitudinal section through the heat exchanger 1. Here too, a plurality of pairs of films 5 and the heat conducting ribs 6 arranged between them can be seen again. A single terminating film 11 is laid as an upper and a lower termination of the heat exchanger 1, onto the bundle stacked alternately from the pairs of films and the heat conducting ribs. In order to ensure that the conduit elements 2, 3 are connected to the respective media spaces 7 and are sealed off relative to the space surrounding the heat exchanger 1, spacers 12 are arranged between the individual pairs of films in the region of the conduit elements 2, 3.

[0026] The housing 4 has, in the plane perpendicular to the inflowing heat transfer medium A or the outflowing heat transfer medium A′, at least approximately the shape of a conduit element, here of a pipeline element of round cross section. The structure consisting of the heat exchanger 1 and the housing 4 can thus be integrated, without further pressure losses, into an already existing pipeline of comparable diameter. At the same time, the cylindrical shape of the housing 4 affords sufficient stability, along with comparatively small wall thicknesses, with the result that costs and weight can be saved.

[0027] It is also possible, however, to introduce the heat exchanger 1 complete, without the housing 4, into a heat transfer medium flow A, or to provide the housing 4 with conduit elements perpendicularly to the depicted direction of flow of the heat transfer medium A or A′, for the supply with the heat transfer medium.

[0028] In the exemplary embodiment illustrated in FIG. 3, guide plates 13 are fitted into the housing 4. The guide plates 13 ensure that the volume flow of the heat transfer medium A flows through the region of the heat exchanger 1 and does not, for example, flow past the heat exchanger 1.

[0029] In the exemplary embodiment illustrated, the heat exchanger 1 is designed to be self-supporting here, as already mentioned above, and is fastened to the two conduit elements 2, 3 in the housing 4. As regards the conduit element 2, the inlet orifice for the medium B to be evaporated and/or superheated, the fastening is, in principle, a fixed bearing 14. The conduit element 2 may, for example, be screwed or welded in the housing 4.

[0030] In this case, the conduit element 3, the outlet orifice for the evaporated and/or superheated medium B′, forms, in principle, a loose bearing 15. By means of the loose bearing 15, it becomes possible for the conduit element 3 (and therefore also for the heat exchanger 1) to move relative to the housing 4. Consequently, elongations in the heat exchanger 1 caused by heating due to the hot heat transfer medium A can be absorbed without pronounced material stresses occurring in the materials of the heat exchanger 1.

[0031] In this case, the loose bearing is formed, in principle, by a conduit element 16 surrounding the conduit element 3. The conduit element 16 has two rigid end pieces 16 a, 16 b, a flexible conduit portion 16 c being arranged between the two rigid end pieces 16 a, 16 b. At the same time, the rigid portion 16 a, facing the housing, of the conduit element 16 is connected (for example welded) firmly to the housing 4. By contrast, the conduit element 3 of the heat exchanger 1 is connected rigidly to the conduit end 16 b uncoupled from the rigid conduit end 16 a by the flexible conduit portion 16 c. This connection, too, may, for example, be a welded connection. When the heat exchanger 1 is elongated, then, its change in length in the housing 4 can be compensated via the loose bearing 15 or by the flexible conduit portion 16 c. Material stresses due to the thermal elongation of the heat exchanger 1 are thereby prevented.

[0032] The design of the heat exchanger has, in this case, great flexibility, since only the number of pairs of films 5 and heat conducting ribs 6 need be adapted to accommodate a desired output to be transmitted. In principle, the heat exchanger 1 can then be inserted into any conduit element, as the housing 4, with a diameter suitable for this purpose, and can therefore easily be integrated into an existing system.

[0033] By virtue of the size differences between the comparatively small depressions 8 of the media space 7 and the comparatively large heat conducting ribs 6, a highly dynamic response behavior of the heat exchanger 1 can be achieved even, for example in the event of abrupt load changes or changes in the media quantity of the medium B to be evaporated. At the same time, the pressure loss on the heat transfer medium side is reduced.

[0034] The device described is used preferably in fuel-cell systems for the evaporation and/or superheating of educts. From these evaporated educts, preferably a hydrocarbon or hydrocarbon/water mixture, the hydrogen required for the fuel cell is then generated in a so-called gas generation system. In this case, preferably, the waste gas from the fuel cell is used on the heat transfer medium side.

[0035] The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof. 

What is claimed is:
 1. A heat exchanger for evaporating or superheating a medium, having a heat exchange body, comprising: at least one pair of films having a media space formed therebetween in a media side region of said heat exchanger; and at least one inlet orifice and one outlet orifice, each connected to the media space between the at least one pair of films; wherein the media-side region is in thermally conductive contact with a region of said heat exchanger located on a heat transfer medium side of said films; the media space between the two films is formed by depressions introduced on a medium-facing side of at least one of the films of said at least one pair of films; a surface facing away from the medium, in each case of at least one of the films of the at least one pair of films is provided with heat conducting ribs; and a height of the heat conducting ribs is greater than a depth of the depressions.
 2. The heat exchanger according to claim 1 , wherein the heat conducting ribs are arranged on at least one side of the respective pairs of films; and the heat conducting ribs have a corrugated configuration.
 3. The heat exchanger according to claim 1 , further comprising means for fastening the heat exchanger in a self-supporting manner in a heat transfer medium volume flow by means of conduit elements forming inlet and outlet orifices.
 4. The heat exchanger according to claim 1 , further comprising a substantially cylindrical housing.
 5. The heat exchanger according to claim 4 , wherein the housing has guide plates.
 6. The heat exchanger according to claim 3 , wherein the heat exchanger body is received on one of the conduit elements by means of a fixed bearing and on the other conduit element by means of a loose bearing.
 7. The heat exchanger according to claim 6 , wherein the conduit element received via the loose bearing is surrounded by a further conduit element connected to the housing, this conduit element having at least one flexible conduit portion in a direction of flow, and the conduit element being fastened to the conduit element surrounding the conduit element, on that side of the flexible portion which faces away from the heat exchanger.
 8. The heat exchanger according to claim 1 , wherein said medium comprises one of a hydrocarbon and a hydrocarbon/gas mixture for a gas generator for a fuel cell system.
 9. A heat exchanger for heating of a fluid medium by thermal contact with a heat transfer medium comprising: at least one pair of films; a media space formed between said at least one pair of films on a media side thereof for accommodating a flow of said fluid medium; a heat transfer medium space disposed on heat transfer medium sides of said at least one pair of films opposite said media side, for accommodating a flow of said heat transfer medium; a plurality of heat conducting ribs formed on said heat transfer medium sides of said films in said heat transfer medium space; wherein the heat transfer medium space is in thermal contact with said media space; the media space comprises a plurality of elongate grooves formed on the media side of at least one of said at least one pair of films; and a height of the heat conducting ribs is greater than a depth of the grooves. 